1. Field of the Invention
The present invention relates to a control system for arc welding. Such arc welding may be used to weld all types of steels, cast iron, cast steel and non-ferrous materials, such as, for example, aluminum.
2. Background Art
It is well known in the art that the following circuits can be used for conventional power sources for steady direct current welding: a) an uncontrolled bridge converter with a transformer with tapping wherein the DC output voltage is varied by means of the tapping See, generally, Baun, L. and Fichter, V.: Der Schutzgasschweisser, Teil II: MIG-/MAG-Schweissen, Deutscher Verlag fuer Schweisstechnik (DVS) GmbH, Duesseldorf, 1990, p. 23; b) half/fully-controlled bridge converter with a transformer having a constant transformer ratio. The DC output voltage can be changed continuously by varying the firing angle of the thyristors. generally, Baum, L. and Fichter, V.: Der Schutzgasschweisser, Teil II: MIG-/MAG-Schweissen, Deutscher Verlag fuer Schweisstechnik (DVS) GmbH, Duesseldorf, 1990, p. 25; or c) a combination of a transformer with tapping and a half/fully-controlled bridge converter. See, generally, Munske, H.; Handbuch des Schutzgasschweissens, Teil II; Elektrotechnische Grundlagen-Schweissanlagen und Einstellpraxis, Deutscher Verlag fuer Schweisstechnik (DVS) GmbH, Duesseldorf, 1970, p. 61.
In addition to the above-described steady direct current welding, pulsed direct current welding is also known in the prior art. In particular the power source for pulsed DC welding generally comprises two parallel-connected converters, wherein each may be connected to separate transformers with tapping, or both may be connected to a single transformer with a constant transformation ratio. A three-phase uncontrolled/half-/fully-controlled bridge converter generates the background direct current and the single-phase converter produces the pulsed direct current. The values of the background and pulsed direct current can be determined by the transformation ratios of the transformers and/or by the firing angle of the thyristors. The Pulse frequencies that can be derived from this power source are 25, 33 1/3, 50 and 100 Hz. The Pulsewidth can be changed by altering the firing angle .alpha. of the thyristors of the single-phase converter. See, generally, Baum, L. and Fichter, V.; Der Schutzgasschweisser, Teil II; MIG-/MAG-Schweissen, Deutscher Verlag fuer Schweisstechnik (DVS) GmbH, Duesseldorf, 1990, p. 26; and Munske, H.; Handbuch des Schutzgasschweissens, Teil II; Elektrotechnische Grundlagen-Schweissanlagen und Einstellpraxis, Deutscher Verlag fuer Schweisstechnik (DVS) GmbH, Duesseldorf, 1970, p. 87.
Both of the above-identified power sources produce harmonics in the AC mains. In particular, in the case of a DC pulsed current welding power source, the single-phase converter causes distortion in the AC mains and low dynamic response. Further, disadvantages associated with pulsed power source include, but are limited to, high power loss, low efficiency, large weight and volume, the requirement of more electrical components (and the associated complexity thereof). All of these features serve to render such device complex to operate and maintain.
Thus, it is an object of the present invention to provide a control system which enables steady and pulsed direct current, with a three-phase converter having fewer electrical components and while exhibiting a relatively high dynamic response. Moreover, it is further an object of the present invention to compensate for the distortions in the AC mains.
Indeed, through such a system as will be explained, it is possible to weld both with steady and pulsed direct current with a single three-phase converter having fewer electrical components and a high dynamic response. With such a system, the power source can be easily constructed and further, it occupies less space as compared to the known systems in the art. Moreover, it provides a simple over-current protection and it can be used for serial production. The distortions in the AC mains are kept minimum with the use of filters.
Additional advantages of the invention will become clear in light of the Specification and Claims.